<style>
    .container {
        max-width: 800px;
        margin: 0 auto;
    }

    .container:after {
        content: "";
        display: block;
        clear: both;
    }

    .container img {
        width: 50%;
        height: 260px;
        float: left;
    }
</style>
<div class="container">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
    <img src="http://s4.sinaimg.cn/mw690/006uWPTUgy72CNFYNjB93&690" alt="1"
    data-src="http://img4.imgtn.bdimg.com/it/u=1878067600,3935137756&fm=200&gp=0.jpg">
</div>
<script>
    // 一开始没有滚动的时候，出现在视窗中的图片也会加载
    start();
    // 当页面开始滚动的时候，遍历图片，如果图片出现在视窗中，就加载图片
    var clock; //函数节流
    $(window).on('scroll', function () {
        if (clock) {
            clearTimeout(clock);
        }
        clock = setTimeout(function () {
            start()
        }, 200)
    })

    function start() {
        $('.container img').not('[data-isLoading]').each(function () {
            if (isShow($(this))) {
                loadImg($(this));
            }
        })
    }
    // 判断图片是否出现在视窗的函数
    function isShow($node) {
        return $node.offset().top <= $(window).height() + $(window).scrollTop();
    }
    // 加载图片的函数，就是把自定义属性data-src 存储的真正的图片地址，赋值给src
    function loadImg($img) {
        $img.attr('src', $img.attr('data-src'));
        // 已经加载的图片，我给它设置一个属性，值为1，作为标识
        // 弄这个的初衷是因为，每次滚动的时候，所有的图片都会遍历一遍，这样有点浪费，所以做个标识，滚动的时候只遍历哪些还没有加载的图片
        $img.attr('data-isLoading', 1);
    }
</script>
